The (K, Na)NbO3 (KNN) of the alkali metal niobate system has become a research hotspot of leadfree piezoelectric materials because of its high voltage constant(d33), high electromechanical coupling coefficient, high quality factor and high Curie temperature (TC). In order to explore the preparation and application of high performance KNN leadfree piezoelectric ceramics, the related preparation process and properties are reviewed with emphasis on the doping, sintering, polarization and their effects on properties. It is pointed out that the doping modification and process optimization of KNN leadfree piezoelectric ceramics are the effective research directions.